AQL sampling is the key to ensuring that random product inspection actually works.
In addition to introducing what AQL is and how to use the AQL tables. We have put together everything you need to know about AQL sampling into chapters that go from easy to in-depth in this article.
AQL for Beginners: Chapter 1 and 2
AQL for Experienced importers: Chapter 3 and 4
AQL for Expert Importers: Chapter 5, 6 and 7
In fact, this is a simplified version of the resource we use for our quality control inspector orientation training before they can provide product inspection service to our clients.
Without further delay, let’s get started!
Table of Contents
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What Does AQL Stand For?
AQL stands for Acceptance Quality Limit and is defined in ISO 2859-1 as “The quality level that is the worst tolerable”.
Based on the total product quantity and your requirements, AQL tells you the maximum number of acceptable defective samples, and you should reject the entire shipment if it is more than that.
AQL sampling is a quality judgment method that originated from the ISO 2859 document issued by the International Standards Organization (ISO) and has corresponding standards in various countries around the world: ANSI/ASQC Z1.4 (USA), MIL-STD-105E (USA), BS 6001 (UK), GB/T 2828.1 (China).
How Does AQL Sampling Work？
AQL sampling means taking samples randomly from the goods following the AQL standard and considering the acceptability of the whole batch of goods according to the quality level of the samples.
A product quality inspection conducted based on the “Acceptance Quality Limit” provides a reliable basis for buyers to decide whether to accept or reject the goods.
What Are AQL Tables (Charts) And How to Read Them (AQL Glossary)?
The AQL tables (or ANSI tables) are a tool to determine sampling plans under the AQL standard for quality inspection participants.
A complete set of AQL sampling tables consists of two tables.
AQL Table 1 – Sample Size Code Letters
AQL Table 2 – Sampling and Acceptance Limits
Most importers only know the concept of AQL, but they don’t know how exactly it works. In fact, the AQL sampling tables are not complicated, and let’s explain the terms on the tables one by one:
Lot Size (AQL Table 1)
Lot size refers to the number of items manufactured for a single production run. In other words, lot size is basically the total number of items ordered to be manufactured.
You can choose the corresponding lot size from different ranges on the leftmost side of the first AQL sampling table. For example, if your order quantity is 1500 pieces, then the corresponding lot size range you should select is “1201 to 3200”.
Finding the corresponding lot size in AQL table 1
Inspection Levels (AQL table 1)
Inspection level is a variable used in the AQL sampling standard to specify the relative amount of inspection. In a nutshell, higher levels check more samples.
In AQL table 1, there are 3 general inspection levels and 4 special inspection levels to choose from. In most cases, you can keep general inspection level 2 as default.
We have a dedicated section onchoosing the right inspection levelif you want to know the difference between all kinds of inspection levels.
Sample Size Code Letter (AQL Table 1)
The sample size is the number of samples randomly selected from the current batch of goods. In AQL table 1, the sample sizes are represented by alphabet letters (Code Letters).
If you have already determined the Lot Size and Inspection Level, you can use AQL table 1 to find the Sample Size Code Letter.
Acceptance Quality Limits (AQL Table 2)
The acceptance quality limits in Table 2 shows different AQL limit values in %
The acceptance quality limits in AQL Table 2 show different values from 0.065 to 6.5. They are given in percent (%) and refer to the proportion of the number of defects to the total lot size.
You can also jump tohow to choose acceptance quality limits (when to reject the goods)
AC and Re (AQL Table 2)
The term “Ac” refers to “accept”, which is the maximum number of defective units in the batch that can still be considered acceptable. And “Re” refers to “reject”, representing the number of rejected sampling lots.
AQL table 2 defines clear acceptance and rejection points for each AQL level through “Ac” and “Re“.
The Arrows in AQL Table 2
There are two types of arrows inside AQL table 2: up and down. If instead of specific ac and re numbers, you find arrows through the Sample Size (Y-axis) and AQL (X-axis) junction, then you should use the first sampling plan pointed by the arrow.
After switching to the arrow-pointed sampling plan, if the new sample size equals or exceeds the Lot Size, conduct a 100% full inspection.
Normal Inspection in AQL Sampling
Normal Inspection is a type of inspection severity in the AQL standard. There are three types of inspection severity in AQL: Reduced Inspection, Normal Inspection and Tightened Inspection.
Important: Normal Inspection is not aninspection level, don’t confuse it withgeneral inspection level 2.
If one or more batches are not accepted in the inspection of consecutive batches, we should move to a higher inspection severity in the inspection of the next batches.
Simply put, a higher inspection severity has a lower acceptance point for the number of nonconformities.
Single sampling plan
Single sampling plan: It means that the decision of accepting or rejecting a lot is based on one-time sampling.
In addition to the single sampling plan, which is the common type of sampling plan, there is also the double sampling plan, which is used to reduce the sample size without increasing the quality risk.
How to Use AQL Table and Calculate the Sample Size (Step by Step Example)
Let’s go through an example of how to calculate the AQL sample size, acceptance and rejection numbers using the AQL tables.
Let’s say you produce a batch of printed T-shirts, one color, in 3 sizes, in a factory in Dongguan, China. Each size is 300 pieces, and the total order quantity is 900 pieces.
Step 1, choose the inspection level
T-shirts are general consumer goods, for workmanship and conformity checks, you can choose the industry default general inspection level 2.
Step 2, match the corresponding lot size range
The only difference between the three T-shirt SKUs is the size therefore you can use the combined quantity of 900 to find the corresponding lot size, which is 501 to 1200
Step 3, find the sample size code letter according to the inspection level and lot size
With the general inspection level II and the lot size of 501 to 1200, we can know the sample size code letter is J.
Step 4, select AQL limits
We need to specify AQL limits for three types of defects: critical, major, and minor. Usually, they are 0, 2.5, 4.0
Step 5, finalize the sampling plan: sample size, acceptance and rejection points
A complete AQL inspection sampling plan includes sample size, acceptance points and rejection points.
The sample size code letter “J” refers to a sample size of 80, so what are the acceptance and rejection points for each of the three defects?
Critical defect:Although the AQL tables do not show an AQL limit of 0, it means that no critical defects are allowed.
Major defect:With a sample size of 80 and an acceptance quality limit of 2.5, we can get the acceptance number to be 5, and the rejection number is 6.
Finding the acceptance and rejection numbers of MAJOR defects using AQL tables
Minor defect:With a sample size of 80 and an acceptance quality limit of 4.0, we can get an acceptance number of 7 and a rejection number of 8.
Finding the acceptance and rejection numbers for MINOR defects using AQL tables
How to Choose AQL Inspection Levels for Your Quality Inspection (How Many Samples to Draw?)
You already know that the AQL inspection level determines the sample size, so how should you choose from the different inspection levels?
The AQL sampling standard has two groups of inspection levels: thegeneral inspection leveland thespecial inspection level. Let’s go into detail：
General Inspection Levels in AQL Sampling Standard
As the name implies, general inspection level is the inspection level used in general to designate how many samples to draw from a product batch. There are three general inspection levels: Levels I, II (default), and III.
Level I may be used when less discrimination is needed or level III when greater discrimination is required. — INTERNATIONAL STANDARD IS0 2859-1
What exactly does“discrimination”mean in AQL sampling? My understanding is “the awareness level about the whole batch quality.”
I know you’re still confused. Let’s go deeper and talk about how you should choose from these three general inspection levels.
General Inspection Level I (G1 / GI)
The G1 level requires the smallest sample size for the same batch quantity among three general inspection levels.
In the following cases, you may consider the inspection level I:
- Your product is manufactured by automated production lines with little human involvement.
- You have a very limited inspection cost budget and inspection time.
- The product is of low value and has a relatively high tolerance for defects.
- Your product has a low potential risk of quality problems.
General Inspection Level II (G2 / GII)
Level II is the default inspection level for general use and is the most common choice for importers.
Suppose one of your suppliers has several batches of goods scheduled for delivery after inspection. In that case, we recommend choosing Level II for the pre-shipment inspection of the first batch as a start.
With the first batch level 2-based inspection results, you can decide whether it is necessary to increase(G3 level) or decrease(G1 level) the sample size of the next batch, or keep the default inspection level.
General Inspection Level III (G3 / GIII )
At the G3 level, the number of samples taken by the quality inspector is the largest of all inspection levels.
By increasing the sample size, Level 3 reduces the risk of undetected defects. However, since product inspectors need to check more samples, the cost of inspection and the time required increase accordingly.
You may want to consider Level III when:
- Supplier product quality is inconsistent.
- You want to improve the quality positioning of your brand
- High product value
- The product is closely related to life safety and health
- This batch is the first mass production of a new product design
Special Inspection Levels in AQL Sampling Standard
Special inspection level is a level of inspection used to determine the number of samples under special situations, which includes four types: S-1, S-2, S-3 and S-4
Four additional special levels, S-1 , S-2, S-3 and S-4 are also given in Table 1 and may be used where relatively small sample sizes are necessary and larger sampling risks can be tolerated. — INTERNATIONAL STANDARD IS0 2859-1
So when do we use the special inspection level instead of the general inspection level for AQL sampling?
The general inspection level is used to determine the sample size for workmanship check and specification conformity verification, while the special inspection level is used to determine the sample size for special tests in AQL inspection.
A third-party inspection company will use a special inspection level to determine how many samples to inspect in the following cases:
- When the tests are time-consuming, 💡e.g., light bulb aging tests
- When the checks are destructive to the product, 💡e.g., internal structure checks of ultrasonic sealed plastic housing products
- When a small number of samples is sufficient to understand the situation, 💡e.g., stop pass gauge testing
How to Select Acceptance Quality Limits in 3 Steps (When to Reject the Goods)?
After knowing the way to decide how many samples to take by choosing the right inspection level, we also need to specify what quality is unacceptable.
Remember that the AQL standard defines the entire shipment’s acceptable quality level by limiting the maximum number of faulty samples that are found from the pulled samples.
Without further delay, follow me throughthree simple stepsto choose the right AQL for your product inspection.
Step 1: Setting Acceptance Quality Limits for the Three Types of Defects
During an AQL sampling random inspection, the inspector may find many defects in the samples taken.
However, the nature and severity of these product defects can be different. In order to efficiently manage defects with varying potential risks, third-party quality inspection companies will classify the various defects into three types.
The most common methods of defect classification are：
Critical defectsare defects that can potentially endanger the personal safety or health of the end-user.
Critical defect example: loose small parts on plush toys (nose of teddy bears, buttons, etc.)
Major defectsare those that affect the intended use of the product.
Major defect example: scratch on the front of the leather sofa
Minor defectsare nonconformities that do not affect the product’s functionalities but do not meet the standards.
Minor defect example: dirty stains on wireless mouse packaging
So what is the AQL value corresponding to these three types of defects?
For general consumer goods, the default international acceptance quality limit standards for three defects categories are 0, 2.5, 4.0, i.e.
for critical defects means thatNOcritical defects are allowed in the AQL sample according to the buyer.
for major defects means that the buyer considers a defect rate of5%of the total order volume for major defects to be the acceptable quality limit.
for minor defects means that the buyer considers a defect rate of0%of the total order volume for minor defects to be the acceptable quality limit.
As an importer, do you have to follow the 0, 2.5, 4.0 AQL standards?
The answer is no, this is just the regular practice, you can also make adjustments according to yourbrand positioningandproduct categories.
Step 2: Review Acceptable Quality Limits Based on Your Brand Positioning
For the same type of product, you may feel that the product quality of a certain brand is better than the other. When further tracing the reason, you will find that their AQL standards (acceptance points) are different.
For example, many of Uniqlo’s SKUs are produced in China, and the average defective rate in the apparel industry is generally 2-3%. In comparison, Uniqlo requires factories to reduce the defective rate to 0.3%.
Moreover, Uniqlo’s rules for evaluating defective products are also stringent. They consider a 0.5mm thread on the surface of T-shirts a defect.
But Uniqlo didn’t get to where it is today in one day, so how should you set the AQL(acceptance quality limit) for your brand?
Here are some tips(questions to ask yourself) to help you figure out how to set a reasonable AQL for your brand (remember: too strict or too low an AQL standard can hurt your brand)：
- What are the brand positioning and your average product gross margin?
- What is your production scale?
- What are the additional costs associated with choosing a higher AQL standard?
- What is the lead time after choosing a higher AQL standard?
- If you have limited resources, is devoting them to achieving a lower-than-industry defective rate the best option for leveraging resources?
Step 3: Identify Product Categories and Industries That Are Closely Related to Life Safety Before Setting AQL
The above two steps for setting up AQL apply to the general consumer goods industry, e.g.
However, suppose your industry or certain product lines operating under your brand are closely related to life safety. In that case, you need to adhere to more stringent rules for setting acceptable quality limits. These industries include but are not limited to:
- Aerospace industry
- Nuclear industry
- Food industry
- Automotive industry
- Military-supplied products
- Medical equipment
Frequently Asked Questions about Acceptable Quality Limits（AQL）
Can AQL inspection guarantee that my goods have zero defects?
The answer is NO. The AQL sampling approach was not intended to achieve zero defects. If you want to achieve zero defects, you can consider 100% full inspection.
AQL inspection is meant to effectively detect and reject substandard product batches through a reasonable amount of inspection effort.
However, instead of setting uneconomical quality expectations like zero defects, experienced importers specify lower AQL acceptance points for their premium brands, meaning that they only allow a very small number of defects in their large production runs.
AQL Sampling Random Inspection vs. 100% Full Inspection, Which One Is Better?
Some novice importers think that a product inspection is to check all the products piece by piece.
The truth is, 100% full inspection is done only on rare occasions. More often than not, importers assign third-party quality companies to conduct random inspections based on AQL sampling standards.
Why is the AQL random inspection more popular than the 100% inspection?
Compared to a full inspection, AQL sampling random inspection has these benefits.
- You do not need to pay the high cost of 100% inspection
- You do not need to wait a long time for the inspection results
- Less packaging damage caused by inspection
- Lower labor costs for repackaging due to inspection
However, AQL random inspection has its drawbacks. Theoretically, random sampling does not guarantee that the goods are free of defects. And that is where 100% inspection comes into play.
Generally, you may want to do a 100% full inspection if:
The cost of defective products entering distribution market is much higher than the inspection cost:For example, some Amazon sellers will do a full inspection of the first shipment into the FBA center at the beginning of setting up a new listing, because in the beginning, a bad review from a defective product can ruin the whole effort.
The first inspection fails, and you don’t think the supplier has reworked it correctly (even if they claim they did):Some suppliers do not have a proper quality control system in place, and you cannot rely on their internal QC process to correct all defects, and sometimes, they do not even quarantine defective products found by the inspector from the major shipment.
More articles to make your import business better:
(9 Methods) How To Know If Alibaba Supplier Is Legit In 5 Mins
What Is Alibaba Multispecialty Supplier? What Does It Mean to You?
AQL Sampling 101: Meaning, Tables, Levels for Inspection
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